Field of the Invention
The present invention relates to a method for producing a modified polymer or a hydrogenated product thereof.
Discussion of the Background
A polymer or a copolymer having different properties or the like can be produced using a conjugated diene and an aromatic vinyl compound by changing the content of the aromatic vinyl compound or the like, and has been used in various applications. Such a polymer or copolymer is normally produced by solution polymerization that uses a hydrocarbon-based solvent or the like and an active organometal catalyst or the like as a polymerization initiator. It is necessary to use a high-purity raw material (monomer) and a high-purity polymerization solvent for solution polymerization since impurities affect the polymerization reaction. However, the solvent recovered after polymerization includes light components such as water, unreacted monomer, an alcohol, and an aldehyde, and heavy components such as a low-molecular-weight polymer (e.g., oligomer) and various additives (e.g., antioxidant). It is undesirable to recycle the recovered solvent directly for polymerization.
A functional group may be introduced into the main chain, the side chain, or the molecular end of the above polymer or copolymer during production using the modification method described later in order to provide various properties. A functional group that includes an active proton (e.g., amino group or mercapto group) is useful as the functional group although the desirable functional group differs depending on the properties required for the modified polymer or the copolymer. However, when a compound having an active proton is added to the reaction solution, the polymerization active end may be inactivated due to the active proton. In order to deal with the above problem, a method has been proposed that introduces a functional group into a polymer using a compound in which an active proton is protected with a silyl group, and effects hydrolysis using an appropriate method to obtain a modified polymer or a modified copolymer that includes a functional group having an active proton. In this case, a silanol compound is included in a solvent to be recovered.
A functional group-containing compound used to incorporate a functional group in the main chain, the side chain, or the molecular end of a polymer is referred hereinafter to as “modifier”. Note that three modification methods may be used as described later, and the term “modifier” is used as a generic name for an initiator, a functional group-introducing monomer, or a polymerization terminator having a functional group.
When a silanol compound is included in a polymerization solvent, polymerization is inhibited by the silanol compound. When the content of the silanol compound is low, the silanol compound can be made harmless by increasing the amount of the polymerization initiator to produce a metal silanolate, for example. However, since a silanol compound is produced when the reaction solution containing the metal silanolate is brought into contact with water in a solvent removal step using a steam stripping method or the like, the solvent to be recovered includes silanol compounds derived from the modifier and the metal silanolate. Therefore, when the solvent is repeatedly recycled, the silanol compound concentration in the solvent increases, and it becomes difficult to make the silanol compound harmless by increasing the amount of the polymerization initiator, for example. In this case, the recovered solvent cannot be recycled as a polymerization solvent. Therefore, it is necessary to remove the silanol compound in order to recycle the recovered solvent for polymerization when producing a modified polymer or a hydrogenated product thereof.
The hydrogenated product is obtained by hydrogenating the modified polymer or the copolymer using a normal method, and the silanol compound is included in the solvent recovered using a steam stripping method or the like.
It is necessary to remove a component that inhibits polymerization when recycling the recovered solvent as a polymerization solvent. For example, a method has been known that washes a hydrocarbon-based solvent separated from a polymer with water, followed by dehydration to remove a lower alcohol used as a polymerization terminator, and recycles at least part of the hydrocarbon-based solvent for a polymerization reaction (see JP-A H9-255716, for example). According to the method disclosed in JP-A H9-255716 that removes a lower alcohol through washing with water and dehydration, it is possible to remove a silanol compound in addition to a lower alcohol by optimizing the volume of water used for washing. The method needs to treat the entire solvent. A method that removes a silanol compound through adsorption on alumina has also been known (see WO2010/056694, for example).